Titanium and/or zirconium nitride based articles of jewelry

ABSTRACT

FINE-GRAINED MIXTURE OF 30 TO 99 VOLUME PERCENT REFRACTORY NITRIDE, 0 TO 45 VOLUME PERCENT REFRACTORY OXIDES, BORIDES OR CARBIDES, AND 0 TO 50 VOLUME PERCENT METAL ARE SINTERED OR HOT-PRESSED TO FORM ARTICLES OF JEWELRY HAVING LOW POROSITY, A GOLDEN COLOR, PERSPIRATION RESISTANCE AND A HIGH LUSTER WHEN POLISHED.

3,669,695 TITANIUM AND/R ZIRCONIUM NITRIDE BASED ARTICLES OF JEWELRYRalph K. Iler, Wilmington, Del., and Alan B. Palmer, Columbia, Md.,assignors to E. I. du Pout de Nemours and Company, Wilmington, Del. NoDrawing. Filed Nov. 21, 1969, Ser. No. 878,890

Int. Cl. C04b 35/52, 37/00; B2213 3/00 US. Cl. 106-43 14 Claims ABSTRACTOF THE DISCLOSURE United States Patent 0 Fine-grained mixture of 30 to99 volume percent re- 7 BACKGROUND OF THE INVENTION This inventionrelates to articles of jewelry which consist essentially of 20 to 100volume percent refractory nitride, 0 to 70 volume percent refractoryoxide, boride or carbides, and 0 to 50 volume percent metal.

Some such compositions are known in the art to possess good hardness andstrength as disclosed in US. Pats. Nos. 3,409,416, 3,409,417, 3,409,418and 3,409,419. We have discovered that the compositions of thisinvention when shaped as articles of jewelry exhibit a number ofunusually desirable characteristics. Refractory carbides have beenemployed in the prior art in making watch cases as disclosed in US. Pat.No. 3,242,664. However, refractory carbides have some drawbacks for usein making articles of jewelry. Most refractory carbides have moderateelectrical conductivity, a limited resistance to acid-corrosion such asthat caused by perspiration, and very high density which makes thearticles of jewelry quite heavy. We have discovered that byincorporating substantial amounts of particular nitrides into thecomposition comprising the articles of jewelry, distinct advantages areobtained. The presence of a nitride of titanium, zirconium, hafnium,niobium, or vanadium increases acidcorrosion resistance and decreasesdensity, resulting in jewelry which resists perspiration corrosion andis light weight. The nitrides also impart a distinct and unusual goldencolor to the jewelry which is quite pleasing to the eye. 'In addition toa pleasing appearance, the articles of this invention are unusuallyscratch-resistant. They can thus be worn for extended periods withoutbeing marred or tarnished. The articles of this invention are also verystrong and tough and are therefore very durable as compared to manynatural and artificial stones and gems used in articles of jewelry.Finally the articles of this invention are quite refractory and thuswill not melt or decompose at high temperatures at which conventionalmetals or alloys would collapse.

SUMMARY In summary this invention relates to articles of jewelry whichcomprise a hard polished composition consisting essentially of 20 to 100volume percent of a nitride of titanium, zirconium, hafnium, niobium,vanadium or their mixtures; 0 to 70 volume percent of a boride orcarbide of titanium, zirconium, niobium, tantalum, tungsten, molybdenum,hafnium, vanadium, or chromium, aluminum nitride, alumina, zirconia,silica, titania, magnesia, magnesium aluminate, the rare earth oxides,or their mix tures; and from 0 to 50 volume percent chromium,moylbdenum, tungsten, iron, cobalt, nickel, titanium, zirconium,niobium, tantalum, hafnium or their mixtures;-said composition having adensity of less than 9 grams per cubic centimeter, a porosity of lessthan 5%, an average grain size of less than 10 microns, a ratio of lightreflectance at 555 millimicrons wavelength to that at 450 millimicronswavelength of between 1.1/1 and 1.6/1, and a resistance to perspirationby corrosion.

Such articles of jewelry are scratch and'mar-resistant, strong, toughand very durable and possess a distinctive golden color.

DESCRIPTION OF THE INVENTION The articles of this invention comprisedense, fine- -grained solids containing 20 to 100 volume percent of arefractory nitride or mixture of refractory nitrides selected from amongthe nitrides of titanium, zirconium, hafnium, niobium, vanadium andtheir mixtures; 0 to volume percent of an electrically non-conductingcomponent selected from among silica, titania, magnesia, aluminumnitride, alumina, zirconia, magnesium aluminate, the rare earth oxidesand their mixtures; 0 to 70 volume percent of an electrically conductingcomponent selected from among the borides and the carbides of titanium,zirconium, niobium, tantalum, tungsten, vanadium, chromium, molybdenum,hafnium and their mixtures; and 0 to 50 volume percent of a metalselected from the group chromium, molybdenum, tungsten, iron, cobalt,nickel, titanium, zirconium, niobium, tantalum or hafnium or mixtures ofthese metals. These solids are characterized by a density of less than 9grams per cubic centimeter, low porosity, a small average grain size, apolished surface which is resistant to acid corrosion such as cuased byhuman perspiration and a ratio of light reflectance at 555 millimicronswavelength which is from 1.1 to 1.6 times as great as the reflectance at450 millimicrons wavelength.

COMPONENTS The articles of this invention comprise dense solids whichconsists essentially of refractory nitrides TiN, ZrN, HfN, NbN, VN ortheir mixtures; optionally AlN, A1 0 ZrO Al O -MgO, SiO TiO' MgO, rareearth oxides or their mixtures; optionally borides or carbides of Ti,Zr, Nb, Ta, W, Mo, V, Cr, Hf or their mixtures; and, optionally, Cr, Mo,W, Fe, Co, Ni, Ti, Zr, Nb, Ta or Hf metals or their mixtures.

(a) Nitrides The essential refractory nitrides suitable for use in thisinvention are titanium nitride, zirconium nitride, hafnium nitride,niobium nitride, vanadium nitride or their mixtures. These nitrides areused in amounts ranging from 20 to 100 volume percent. Because corrosionresistance, lightness and color are increased with increased amounts ofnitrides, it is preferred to use at least 30 volume percent of thenitrides, more preferably 40 volume percent and most preferably 50volume percent. Because the presence of at least some metal binder isdesirable, it is preferred to use no more than 99 volume percentnitride, and to permit for the presence of metal and other components,it is more preferred to use no more than volume percent and it is mostpreferred to use no more than 75 volume percent nitride. For thesereasons it is also preferred to have at least 1 percent metal presentwhen the nitride exceeds percent. Of the nitrides, titanium nitride isthe one most preferred for use in the compositions of this invention,and zirconium nitride is next preferred.

The average particle size of the nitrides used should be less than 5microns and preferably less than about 2 microns. If a starting materialis appreciably larger than 5 microns in particle size, it can bepro-ground to reduce its size to that which is acceptable. Of course,the mixmilling of the various components of the preferred compositions,which is carried out to obtain a high degree of homogeneity, will resultin some comminution of the nitrides as well as the other startingcomponents.

The nitrides to be used in this invention can be prepared by anyconventional method; by nitriding the corresponding finely milledhydrides or metallic elements as described in US. Pat. No. 3,409,416; orby a suitable reaction in a molten salt such as described in US. Pat.No. 3,409,419. The latter is a preferred method because it results innitride particles of an average size of less than a micron.

The nitrides can also be formed by the carbon reduction in the presenceof nitrogen of the corresponding metal oxides in a manner which isdescribed in the literature. Conventional methods for the preparation ofthe essential nitrides of this invention are disclosed, for example, inNitrides, Chapter VIII of a book entitled High Temperature Technology,by John M. Blocher, Ir., John Wiley & Sons, N.Y., 1956.

Representative of suitable commercially available nitrides are -325 meshgrade TiN and ZrN powders available from Materials for Industry, Inc.,Ambler, Pa., as well as the 325 mesh grade TiN, ZrN and HfN powders and--100 mesh grade NbN and VN powders available from ConsolidatedAstronautics, Inc., Long Island City, NY.

(b) Electrically non-conducting components The electricallynon-conducting components which can be used in the compositions of thisinvention are aluminum nitride, alumina, zirconia, silica, titania,magnesia, magnesium aluminate (Al O -MgO), the rare earth oxides andtheir mixtures. These components are used in amounts ranging from to 70volume percent. Preferred amounts of these components are 0 to 50 volumepercent, and most preferably 0 to 35 volume percent and it is preferredto use aluminum nitride or alumina.

Average particle size of these components should generally be less thanabout 5 microns and preferably less than about 2 microns. As statedabove, the preferred oxide is alumina, and preferably its averageparticle size is less than 2 microns, most preferably less than 0.5micron.

If the starting material is appreciably larger than 5 microns inparticle size, it can be pre-ground to reduce its size to that which isacceptable. Of course, as mentioned above, the mix-milling of thecomponents carried out to obtain a high degree of homogeneity, willresult in some comminution of the components.

The electrically non-conducting components suitable for use in thisinvention can be in any form so long as they are finely divided. Thus,for example, alumina can be in the form of gamma, eta or alpha aluminaor their mixtures. Alpha alumina is a preferred form of alumina becauseits specific surface area is lower than gamma or eta alumina and islikely to contain less adsorbed water.

The oxides can be prepared by any of the well-known conventional methodsor they can be obtained commercially. A suitable commercial alumina isAlcoa Superground Alumina XA-l6 with a specific surface area of about 13square meters per gram. Suitable commercial forms of the other oxidesare powders graded 325 mesh such as those available from Materials forIndustry, Inc.

The aluminum nitride can be prepared by any of the conventional methodsdescribed above for the essential nitrides. Representative of suitablecommercially available aluminum nitride is a podwer grade 325 meshavailable from Materials for Industry, Inc.

(c) Carbides and borides The electrically conducting borides andcarbides which can be used in the compositions of this invention are thecarbides and borides of titanium, tungsten, molybdenum, tantalum,zirconium, vanadium, chromium, hafnium, niobium and their mixtures.These carbides and borides can be used in the compositions of thisinvention in amounts of 0 to 70 volume percent. Preferred amounts ofthese components are from 0 to 45 volume percent. It is also preferredto use the carbides of titanium, zirconium or tantalum or titaniumdiboride, and it is most preferred to use titanium carbide.

The carbides and borides suitable for use in this invention should havean average particle size of less than 5 microns and preferably less than2 microns. If the starting material has a particle size appreciablylarger than 5 microns, it can be pre-ground to reduce its size to 5microns or less prior to its use. Of course, the mix-milling of thecomponents, as mentioned above, will result in some comminution of thecomponents.

Suitable carbides and borides can be prepared by means well-known to theart or they can be obtained commercially. Representative of suitablecommercial carbides and borides are the powders graded 325 mesh such asthose available from Materials for Industry, Inc. or from Cerac, Inc.

(d) Metals The metals which can be used in the compositions of thisinvention are molybdenum, tungsten, chromium, iron, nickel, cobalt,titanium, zirconium, niobium, tantalum, hafnium and their mixtures witheach other.

These metals are used in the compositions of this invention in amountsranging from O to 50 volume percent. It is preferred to have at least 1and more preferably 5 volume percent of metal present and preferably nomore than 20, most preferably no more than 15 volume percent of metalbecause in this range there is an optimum balance in chip resistancewhen the pieces are cut and ground, ease of polishing and corrosionresistance.

Of the refractory metals, it is preferred to use molybdenum or tungstenor their mixtures with the iron group metals. Of the iron group metals,nickel is preferred. It is most preferred to use molybdenum or tungstenin combination with Ni.

As stated above, relatively high amounts of metals, up to 50 volumepercent, can be used in the compositions of this invention. However,increases in the metal content of the composition should be coupled withcorresponding increases in the boride, carbide or oxide content tomaintain the corrosion resistance of the compositions. It is believedthat molybdenum metal difluses into the lattice of carbides such astitanium carbide so that if there is sufficient carbide present, therewill be little or no free molybdenum metal present, thereby maintainingthe high resistance to corrosion.

The metals suitable for use in this invention should have an averageparticle size of less than 5 microns and preferably less than 2 microns.If the starting powder has a particle size appreciably larger than 5microns, it can be pre-ground to reduce its size to 5 microns or lessprior to its use. Of course, the mix-milling of the components, asdescribed above, will result in some comminution of the components.

Metal powders with the required size and degree of purity can beobtained from commercial sources or they can be prepared by conventionalmeans. A suitable method of preparation is low temperature hydrogenreduction of the corresponding metal oxide, or hydrogen reduction ofiron, cobalt or nickel carbonate at a temperature between about 600 C.and 1200 C. Such preparations should be carried out at a temperature asis practical to prevent excessive sintering and agglomeration of themetal being formed.

In the preparation of molybdenum and tungsten from their oxides, it isbest to employ a two-stage reduction because of the relative volatilityof some of these oxides. The first-stage reduction is carried out belowthe oxide melting point, such as at 600 C. Then the second-stagereduction is completed at say 900 C.

Metals prepared as described above can be milled in an inert medium toincrease their surface area and can then be purified such as withhydrochloric acid. It is desirable to use grinding media, when millingthe metal, which is made of the same metal as being ground, thecomponents which are to be mixed with the metal, or very wear-resistantmaterial to avoid introducing impurities by attrition of the media.

Representative of suitable commercially available metals are finetungsten powder from General Electric, Detroit, Mich., with a nitrogenspecific surface area of 2 square meters per gram and fine nickel powderavailable from International Nickel Co., with a nitrogen specificsurface area of 0.5 square meter per gram.

(e) Impurities The components to be used in the compositions of thisinvention are preferably quite pure. In particular, it is desired toexclude impurities such as oxygen which would tend to have deleteriouseffects on the dense compositions.

On the other hand, minor amounts of many impurities can be toleratedwith no appreciable loss of properties. Thus the metal can contain smallamounts of other metals, although low melting metals like lead should beexcluded. Small amounts of other carbides can also be present. Evenoxygen can be tolerated in small amounts such as occurs when titaniumcarbide has been exposed to air, resulting in a few percent of titaniumoxy-carbide. However, after the powder components have been milledtogether and are in a highly reactive state, oxidation, particularly ofthe metals, occurs easily and should be avoided.-

PREPARATION OF THE ARTICLES OF THIS INVENTION The preparation ofinterdispersions of the nitrides with the borides, carbides, oxides, ormetals if they are used, in the form of a powder, can be carried out inthe manner disclosed in US. Pat. No. 3,409,416.

The powder interdispersions of the carbides with the oxides, and themetal if they are used, are fabricated by sintering or hot-pressing inthe form of a dense solid, also as described in US. Pat. No. 3,409,416as well as US. Pat. No. 3,413,392 and copending application Ser. No.846,525 filed July 31, 1969.

The dense compositions consisting essentially of nitrides and optionallycontaining oxides, carbides, borides and metal can be shaped intoarticles of jewelry without the use of any other material. Alternativelythe dense compositions can be mounted on a backing such as metal, wood,plastic or cloth, or can be used as a mount for precious or semipreciousstones, gems and minerals. The resulting items of jewelry can be purelydecorative, functional or combine function with decoration.

Items of jewelry are so Well known and the size, shapes, combinations ofmaterials used and areas of use are so broad that it is impossible andshould be uncessary to list all possible types of jewelry for which thecompositions of this invention are suitable. The following abbreviatedlist is merely representative of suitable uses. The compositions of thisinvention can be used alone or in combination with any structuralmaterials or materials of apparel including metal, wood, glass,minerals, plastics, cloth, paper, leather, precious stones, shells, orsynthetic organic or inorganic materials. Combinations can be made forexample by brazing, soldering, gluing, ce-

6 menting, insetting, pegging, and sewing, such jewelry items as thefollowing:

Watch cases Belt buckles Culf links Compacts (cosmetic cases) EarringsCharms for charm bracelets Pins Insignias Rings Pendants Tie tacksCigarette cases Necklaces Metal ornaments Buttons Trophies Clips Bottleopeners Lapel buttons Hairpins Bracelets Shoe buckles Monograms Pillboxes Medals Dress or shirt studs Shoehorns Identification tags Hairornaments Paper weights Methods for fabricating such item of jewelry aswell as methods for cutting, shaping and polishing the densecompositions will be apparent to those skilled in the art and are morefully described in the examples.

CHARACTERIZATION METHODS The compositions of this invention arecharacterized by their visible light reflectance ratio, corrosionresistance to perspiration, high mechanical strength, outstandingtoughness and hardness, density, low porosity, small grain size andhomogeneity of the interdispersion between components.

Determination of mechanical strength and hardness are made byconventional transverse rupture and Rockwell A methods.

Methods for the determination of porosity, grain size and homogeneity ofsolid bodies are described in US. Pat. No. 3,409,416. The composition ofthis invention are characterized by a porosity of less than 5% and anaverage grain size of less than 10 microns. Preferably, compositions ofthis invention have a porosity less than 1% and an average grain size ofless than 2 microns.

Toughness is determined only qualitatively by allowing a finishedfabricated object of this invention to freely fall on a hardwood floorfrom a height of seven feet. The compositions of this invention do notbreak or chip under the conditions of this test.

The actual density of the compositions can be determined by anyrecognized method, most simply by weighing in air, and immersed inwater, a sample which has been previously measured. The water should beboiled before weighing the sample to remove dissolved air. The densityis calculated from the formula weight in airXspecific gravity of waterdensl yweight in airweight in water The theoretical density for thecomposition can be calculated on the basis that the volume for a givenweight of the composition is equal to the sum of the volumes of thecomponents calculated from the weight of each component divided by itsdensity.

The solid bodies of this invention, as pointed out above, have a densityof less than 9 grams per cubic centimeter and since their porosity isgenerally less than 1%, their actual density will ordinarily exceed 99%of their theoretical density.

One of the characteristics that materials should have, to qualify fortheir use in pieces of jewelry that are in continuous contact with theskin, such as rings, bracelets and watch cases, is resistance tocorrosion by human skin excretions. It is known, for example, that inhot climates even stainless steel watch cases can be corroded completelythrough in normal use on the wrist. To evaluate this characteristic, acororsion test using a liquid with the average composition of humanperspiration is employed. A solution is prepared with the compositionstated to be the average composition of human perspiration in NormalValues in Clinical Medicine by -F. W. Sunderman and F. Boerner, W. B.Saunders Co., Philadelphia and London, 1949 at page 488. The compositionis No urea or uric acid, included as traces in the average compositionof human perspiration, are added to the corrosion solution.

The corrosion solution is placed in a beaker in a constant temperaturebath at 40 C. and glass stirrers are used to keep the solution stirringgently.

Test specimens used as corrosion coupons are 0.810 inch x 0.500 inch x0.100 inch in size. They are used as cut with resin-bonded diamondwheels without further grinding or polishing except as needed to conformthe coupons to standard size.

Clean test specimens are accurately weighed and measured and then areimmersed in boiling dimethylformamide for 4 minutes to ensure no surfacecontamination. Upon removal from the dimethylformamide the coupons arerinsed with water and acetone, are dried in a vacuum oven, and aretransferred directly into the corrosion solution.

At measured intervals the specimens are removed from the corrosionliquid, are rinsed with distilled water and acetone, are dried in avacuum oven and are then weighed. They are then re-cleaned in boilingdimethylforamlde, water and acetone and are dried and returned to thecorrosion liquid. Weight loss is calculated per unit of surface area ofthe specimen for the given intervals of time. The surface of somespecimens are examined by optical micrograph before starting the testand at fixed intervals during the test to observe the extent of etching.

The dense compositions of this invention are characterized by a weightloss of less than 5 milligrams per square centimeter after immersion inthe above described synthetic perspiration at 40 C. for ten days. Thisresistance to perspiration corrosion is greater than that ofcobaltbonded tungsten carbide compositions which are currently beingused to make scratch resistant watch cases.

The attractive ornamental appearance of the compositions of thisinvention is one of the most important characteristics for jewelry uses.

The compositions of this invention have a golden appearance due to thedeficiency of blue in the reflected spectrum of visible light (about 400to 700 millimicrons wavelength). The gold color of the compositions ofthis invention range from yellow gold to bronze gold. The color of thesecompositions is characterized by measuring their light reflectance ratioat 555 millimicrons and 450 millimicrons. As the yellow or goldencomponent of the compositions increases, so does the IR /IR ratio. IR isthe percentage of light intensity of 555 millimicron wavelengthreflected and IR is the percentage of 450 millimicron wavelengthreflected light intensity.

Light reflectance measurements of the compositions of this invention areconveniently made by means of the method described below:

A Bausch & Lomb Spectronic 505 spectrophotometer with an integratingsphere attachment is used for the measurements of light reflectance.

The spectra recorded with the Spectronic 505 is obtained usingdirectional illumination and diffuse viewing from the integrated spherewith a trap for the specular reflection.

In the case of diffuse reflection, the integrating sphere collects allthe light reflected diffusely (not the direct mirror reflection) fromthe surface of the sample placed against the opening (called the port)in its side. The integrating sphere is a hollow metal sphere severalinches in diameter painted white inside. Illumination of the sample isadjusted at an angle to the normal such that the specu larly reflectedlight (mirror reflection) is trapped in a light trap, and therefore doesnot contribute to the spectrophotometer readings.

Specimens for light reflectance measurements consist of 1 and /2 inchdiameter circular and 1 and /2 inch x 1 and 75 inch rectangular hotpressed samples with a flat surface, mounted on 2 inch diameter Bakelitesupports flush with the samples. This size of sample is large enough toassure that the surface is within the scope of the instruments lightbeam and that the samples fit the port tight enough to prevent lightlosses.

The surface of the specimen is flat, ground and polished. Polishing isdone first with 400-grit and 1000- grit Vespel resinoid-bonded diamondwheel on 8 inch diameter wheels at 1175 revolutions per minute and 550revolutions per minute, respectively. Final finish is ob tained bypolishing with 6 micron diamond paste using kerosene lubricant and onemicron diamond dust impregnated on a rotating cloth disc and lubricatedwith water.

It is important to make all measurements with samples polished understandard conditions, since the degree of optical smoothness of a surfacedetermines the extent to which incident light is reflected in alldirections. A diffusing surface tends to cause reflection equally in alldirections. Rough or porous surfaces thus tend to cause reflection inall directions. The smoother the surface the more directional is thereflection.

Measurements made by the instrument are obtained in the form of percenttransmission versus light wave length plots. Compositions of thisinvention are characterized by smooth light reflectance curves with nopeaks, but an increasing reflectance from the blue range of the visiblespectrum and a ratio of percent reflectance at 555 millimicrons to thatat 450 millimicrons of between 1.1 to 1 and 1.6 to 1.

UTILITY The jewelry articles comprising compositions of this inventioncan be used in whatever areas items of jewelry are used, either in apurely decorative sense, or to combine practical utility with decorativeadvantages. These jewelry compositions have an unusually pleasingmetallic luster which because of the presence of the nitrides has anunusual golden tone. While the unusual appearance is due to the presenceof the nitride phase, as in most esthetically pleasing effects, thedifference in appearance can be observed with the human eye but isdiflicult to define, to measure or to quantify. Also, as mentionedabove, in contrast to conventional metals, including stainless steels,silver or gold, articles of jewelry comprising the compositions of thisinvention are unusually scratchresistant. By virtue of their fine grainsize and lack of porosity, compositions of this invention can bepolished to an unusually high degree and this polish is not scratched,marred on dulled in even the roughest convenventional use when contactedwith any conventional materials of construction or items of apparelincluding metals, glass, concrete, bricks, Wood, plastics etc. Also,because of their good corrosion resistance, the compositions of thisinvention can be worn for long periods in contact with human skin andperspiration without severe tarnishing. The compositions of thisinvention are stronger and tougher than many materials such as naturalor artificial stones or gems or insets used in jewelry, and so they aremore durable. Since the materials of this invention are extremelyrefractory they will not melt or decompose at high temperatures at whichconventional metals or alloys would collapse. This unusual combinationof properties makes these materials unexpectedly valuable for use inarticles of jewelry.

The following examples illustrate the invention. Parts and percentagesreferred toin the examples are by weight unless otherwise indicated.

EXAMPLE 1 This is an example of a composition containing 50 volumepercent of titanium nitride, 20 volume percent of aluminum oxide, 15volume percent of aluminum nitride, 12 volume percent of tungsten metaland 3 volume percent of nickel metal.

The titanium nitride used is grade 325 mesh powder, available fromMaterials for Industry, Inc., and has a specific surface area of 1.1square meters per gram as determined by nitrogen absorption. An electronmicrograph of the powder shows dense particles of irregular shapes withsizes between 1 and about 10 microns, with the bulk being between 1 and2 microns. The carbon content is 0.33 percent and the oxygen content is0.87 percent. Chemical analysis reveals 76.19 percent of titanium and18.71 percent of nitrogen.

The alumina used is very finely divided alpha alumina, commerciallyavailable as Alcoa Superground Alumina XA-l6 and is characterized byX-ray examination as pure alpha alumina. It has a specific surface areaof about 13 square meters per gram, which is equivalent to a sphericalparticle size of about 115 millimicrons. Under an electron microscopethis alpha alumina powder appears as aggregates of alumina crystals inthe range of 100 to 150 millimicrons in diameter.

The aluminum nitride used is grade -325 mesh powder supplied byMaterials for Industry, Inc., and has a specific surface area of 2.3square meters per gram as measured by nitrogen adsorption. An electronmicrograph shows dense particles of very irregular shape Globularparticles have diameters ranging between 2 and 12 microns and elongatedparticles show a width of 1 to 3 microns and a length between 4 and 16microns. I he carbon content is 0.43 percent and the oxygen content isl.55 percent. The results of chemical analysis show that the powdercontains 63.95 percent aluminum and 32.27 percent nitrogen.

The tungsten used is a fine powder available from General Electric. Ithas a specific surface area of 2.0 square meters per gramand an oxygencontent of 0.19 percent. Crystallite size as measured by X-raydifiraction line broadening techniques is 174 millimicrons.

The nickel used is a fine powder, available from International NickelCo., containing 0.15 percent carbon, 0.07 percent oxygen, and less than300 ppm. iron. The specific surface area of the nickel powder is 0.48square meters per gram and its X-ray diffraction pattern shows onlynickel, which as measured by X-ray line broadening has a crystallitesize of 150 millimicrons. Under electron microscope, the powder appearsas grains 1 to 5 microns in diameter.

The powders are milled by loading 6000 parts of preconditionedcylindrical cobalt-bonded tungsten carbide inserts, A inch long and inchin diameter, into a 1.3 liter steel rolling mill about 6 inches indiameter, also charged with 290 parts of Soltrol 130 saturatedparaifinic hydrocarbon, boiling range 165-210 C. The mill is thencharged with 81.45 parts of titanium nitride, 14.66 parts of aluminumnitride, 23.88 parts of the alpha alumina, 69.33 parts of tungstenpowder, and 9.08 parts of nickel powder, all as above described.

The mill is then sealed and rotated at 90 revolutions per minute for 5days. The mill is then opened and the contents emptied while keeping themilling inserts inside. The mill is then rinsed out with Soltrol 130several times until all of the milled solids are removed.

The milled powder is transferred to a vacuum evaporator, and the excesshydrocarbon is decanted off after the suspended material has settled.The wet residual cake is then dried under vacuum with the application ofheat until the temperature within the evaporator is between 10 200 and300 C., and the pressure is less than about 0.1 millimeter of mercury.Thereafter the powder is handled entirely in the absence of air.

The dry powder is pasesd through a 70 mesh screen in a nitrogenatmosphere, and then stored under nitrogen in sealed plastic containers.

A watch case is prepared from this powder by hot pressing the powder ina graphite mold assembly designed in such a way as to permit hotpressing the powder in the shape of a ring with a round hole of a sizeinto which the encased operating works of a Watch can later bepress-fitted, the ring serving as a protective and decorative case. Thegraphite mold consists of a 4 inch long hollow cylinder of graphite withan outside diameter of 2 and /2 inches, the cross-section of the cavitybeing in the shape of a square with rounded sides. The maximum insidediameter of the cylinder is 2 inches. A hollow piston is placed into thebottom end of the cylindrical mold, the outside diameter of the pistonfitting snugly into the inside diameter shape of the mold. The pistonhas a cylindrical cavity with a 1 and inch round cross-section. The endof the piston in the mold is tapered or dished so that the bottom of thering to be formed from the powder will have a somewhat decorativerounded surface rather than a flat surface. A third hollow cylinder withan outside diameter of about 1 and inch and a wall thickness of inchfits snugly into the hollow piston and extends up beyond the piston intothe mold. Finally, a solid rod fits into the thin-walled inner cylinderto keep it from collapsing during the pressing operation. A weighedportion of 32 parts of powder, calculated to result in a completelydense pressed piece with the proper thickness, is poured into the moldand the mold it tapped so that the powder packs in the cavity formed bythe inner wall of the mold, the outer surface of the thinwalledcylindrical spacer and the upper hollowed end of the bottom piston. Asecond hollow piston is then fitted into the assembly from the top toprovide the upper surface for the powder cavity. The entire assembly isplaced into a hot press, and is heated quickly to 1000 C. and then to1800 C. in 10 minutes. The temperature is held at 1800 C. for 2 minutesand then 5000 pounds per square inch pressure is applied through top andbottom solid graphite rams acting on the outer ends of the hollowpistons which protrude from the top and bottom of the mold. Pressure ismaintained for 4 minutes and then the heat is cut off and the pressureis released. The mold is then removed immediately from the hot zone andthe solid rod spacer is permitted to slide out of the center of theassembly. As the mold cools, the pressed watch case ring contracts morethan the graphite. If the solid rod is left in place, the ring wouldfracture from strains set up. Instead, the shrinking ring compresses thethinwalled graphite cylinder which remains in the hole, and the cylindercracks instead of the ring. The thin-walled cylinder is used simply topermit initial easy withdrawal of the solid rod which otherwise would beheld up by sticking to the ring. After the mold has cooled, the pistonsand the ring are removed, by pressure if needed.

The watch case is polished by pressing its faces firmly against rotatingdiamond impregnated cloth discs. A Buehler, Ltd. machine is used in thisoperation for polishing the sample. A 400 grit diamond wheel is used at1175 revolutions per minute in the first polishing step and a 1000 gritdiamond at 550 revolutions per minute is used in a second, finishingstep.

The finished watch case fabricated in this manner has an attractivegolden color.

:"EXAMPIJE 2 The procedure of Example 1 is repeated except that noalumina is used and the rest of the components are used in amounts togive a composition containing 50 volume percent titanium nitride, 30volume percent alu- 1 l minum nitride, 18 volume percent tugnsten and 2volume percent nickel.

The actual amounts of components loaded into the 1.3 liter steel millare 81.5 parts of titanium nitride, 29.3 parts of AlN, 104 parts oftungsten metal, and 5.4 parts of nickel metal.

A consolidated billet is prepared from the powder by hot pressing thepowder in a cylindrical graphite mold having a cavity with a squarecross-section of l and inches x 1 and inches and fitted with opposingclosefitting pistons. One piston is held in place in one end of the moldcavity while 40 parts of the powder are dropped into the cavity undernitrogen and evenly distributed by rotating the mold and tapping itlightly on the side. The upper piston is then put in place under handpressure. The assembled mold and contents are then placed in a vacuumchamber of a vacuum hot press, the mold is held in a vertical position,and the pistons extending above and below are engaged between opposinggraphite rams of the press under pressure of about 600 pounds per squareinch. Within a period of a minute the mold is raised into the hot zoneof the furnace at 1175 C. and at once the furnace temperature isincreased while the positions of the rams are locked so as to preventfurther movement during the heatup period. The temperature is raisedfrom 1l75 to 1800" C. in 10 minutes, and the temperature of the mold isheld at 1800 C. for another 2 minutes to ensure uniform heating of thesample. A pressure of 4000 pounds per square inch is then appliedthrough the pistons for four minutes. Immediately after pressing, themold and contents, still being held between the opposing rams, is movedout of the furnace into a cool zone where the mold and contents arecooled to dull red heat in about 5 minutes.

The mold and contents are then removed from the vacuum furnace and thebillet is removed from the mold and sand blasted to remove any adheringcarbon.

Density of the finished piece as determined by accurate weighing andmeasurement of the dimensions is 7.25 grams per cubic centimeter.

The hot pressed composition is nonporous, having no visible porosityunder 1000 magnification. This property is important since nonporousmaterials are more corrosion resistant than porous materials of the samechemical composition. Structurally the composition consists of anextremely fine co-continuous interpenetrating network of titaniumnitride, aluminum nitride, and metal alloy.

The specimen is so tough that it does not break or chip when droppedfreely to a hardwood [11001' from a height of 7 feet.

Electron micrographs indicate a very fine grain structure, few grainsexceeding 1 or 2 microns in size.

The sample is polished by pressing its faces firmly against rotatingdiamond impregnated cloth discs. A Beuhler polishing machine is employedfor this operation. A 400 grit diamond wheel is used at 1175 revolutionsper minute in the first polishing step and a 1000 grit diamond at 550revolutions per minute is used in a second, finishing step.

The sample polished in this manner has an attractive ornamentalappearance with a golden color.

The polished specimen is used for color measurement with a Bausch andLomb Spectronic 505 spectrophotometer. An eight percent transmittanceversus radiation wavelength curve is obtained by diffuse reflection withthe integrating sphere.

The reflectance curve obtained rises gradually from a flat portion atabout 9.2 percent light reflectance in the violet end of the spectrumbetween 400 and about 435 millimicrons wavelength, to about 15.5 percentlight reflectance in the red end of the visible spectrum. It is thisdeficiency in blue radiations in the reflected light that gives to thematerial its distinctive golden appearance. The reflectance at 450millimicrons is about 9.3

12 percent and at 555 millimicrons is about 12.3 percent for a ratio ofabout 1.3/1.

In addition, the low level of light reflectance even in the yellow tored range of the spectrum makes the material look much darker than goldmetal when fashioned into a tie bar.

EXAMPLE 3 The procedure of Example 1 is repeated except that thecomponents are used in amounts to give a composition containing 50volume percent of titanium nitride, 30 volume percent of alumina, 5volume percent of aluminum nitride, 12 volume percent of tungsten metaland 3 volume percent of nickel metal.

Actual amounts loaded in a 1 gallon steel mill are 299 parts of TiN,131.5 parts of A1 0 18 parts of AlN, 255 parts of W, 29.4 parts of Ni,and 1040 parts of *Soltrol 130.

A square billet prepared as in Example 2, which has a cross-section of 1and inches and about 0.030 inch in thickness, is cut so that specimens0.80 inch x 0.50 inch x 0.10 inch are obtained from its center portion.

These specimens are used as coupons in corrosion tests in a liquid withthe composition of human perspiration as described before. Tests areconducted in a constant temperature bath at 40 C.

The test is carried out by allowing the specimens to stay in thecorrosion liquid for a measured length of time, then removing, rinsingwith water and acetone, drying in a vacuum oven and weighing. tAfterweighing, the specimens are cleaned in boiling dimethylforrnamide,rinsed in water and acetone, and when dried, replaced in the corrosionliquid. The above-mentioned procedure is repeated for various lengths oftime.

The corrosion liquid is gently stirred during the test and thetemperature of the liquid is kept at 40 C. in a controlled constanttemperature bath.

After 10 days the average weight loss of the sample is only 1.8milligrams per square centimeter. Under the same test conditions,commercial cemented tungsten carbide Carboloy shows an average weightloss of 25 milligrams per square centimeter.

Optical microscope observations of C'arboloy 90 samples at 740xmagnification, after 10 hours of immersion in the corrosion testsolution under the conditions described, show that the surface has beenextensively etched. On the other hand, the composition of this example,when observed under the optical microscope after 10 hours in thecorrosion test solution, shows only slight surface etching.

A rectangular piece /2 inch x inch is cut from the billet, polished andused as an attractive, ornamental golden inset by cementing it withepoxy resin on a tie clip.

EXAMPLE 4 The procedure of Example 1 is repeated except that thecomponents are used in amounts to give a composition containing 50volume percent zirconium nitride, 30 volume percent aluminum nitride, 18 volume percent molybdenum metal, and 2 volume percent nickel metal.

The zirconium nitride powder used in this preparation is commerciallyavailable from Materials for Industry, Inc., Ambler, Pa. The powder is99.9 percent pure and the particle size is 0.5 to 5 microns.

The aluminum nitride powder and the nickel metal powder used in thispreparation are the same as used in Example 1.

The molybdenum powder used is available from the General Electric Co.and has a grain size of less than 325 mesh, a specific surface area asdetermined by nitrogen adsorption of 0.29 square meter per gram, and anaverage crystallite size of 354 millimicrons as determined by X-raydiifraction line broadening. An electron micrograph shows the molybdenumpowder consists of grains /z to 3 microns in diameter clustered togetherin open aggregates. Chemical analysis of the powder reveals 0.2 percentoxygen and no other impurities over 500 p.p.m.

Amounts of the components loaded into the 1.3 liter mill are 106.35parts of ZrN, 29.35 parts of AlN, 55.07 parts of Mo, and 5.39 parts ofNi.

A watch case prepared with this composition by the procedure of Example1 has an attractive golden appearance and does not break or chip whenallowed to fall freely on a hardwood floor from a height of 7 feet.

EXAMPLE The procedure of Example 1 is repeated, except that thecomponents are used in amounts to give a composition containing 63volume percent titanium nitride, 30 volume percent alumina, 4 volumepercent tungsten metal, and 3 volume percent nickel metal.

The actual amounts loaded in the 1.3 liter steel mill are 101.85 partsof TiN, 35.82 parts of A1 0 23.15 parts of W, and 8 parts of Ni.

A billet prepared as in Example 2 from this hot pressed composition hasa density of 6.15 grams per cubic centimeter, a hardness of 92.2 on theRockwell A scale and a transverse rupture strength of about 146,000pounds per square inch. The billet is very tough and can be dropped froma height of 7 feet on a hardwood floor without breaking or chipping.

The billet is cut so that a W inch x 75 inch rectangular piece isremoved from the center. The rectangular piece ispolished by pressingits face firmly against rotating diamond impregnated cloth discs. ABuehler, Ltd. machine for polishing the sample is used in thisoperation. A 400 grit diamond wheel is used at 1175 revolutions perminute in the first polishing step and a 1000 grit diamond wheel at 550revolutions per minute is used in a second, finishing step.

The rectangular piece polished in this manner has a lustrous goldenappearance and is used as an ornamental inset by cementing it with epoxyresin to the surface of a metal tie clip.

EXAMPLE 6 The procedure of Example 1 is repeated except that thecomponents are used in amounts to give a composition containing 50volume percent titanium nitride, 20 volume percent aluminum nitride, and30 volume percent tungsten metal.

The actual amounts loaded in the 1.3 liter steel mill are 81.44 parts ofTiN, 19.55 parts of AlN, and 174.00 parts of W.

A billet prepared as in Example 2 except that the maximum temperatureused in the hot pressing operation is 1850 (3., has a density of 9.16grams per cubic centimeter and a transverse rupture strength of about160,000 pounds per square inch. The billet is very tough and can bedropped on a hardwood floor from a height of 7 feet without breaking orchipping.

The billet of this composition is cut and polished as in Example 5, toobtain a piece one-half inch square, having a metallic goldenappearance. The square piece is used as an ornamental inset by cementingit with epoxy resin on a medallion.

EXAMPLE 7 The procedure of Example 1 is repeated, except that thecomponents are used in amounts to give a composition containing 50volume percent titanium nitride, 45 volume percent titanium diboride,4.5 volume percent molybdenum metal, and 0.5 volume percent nickel.

The actual amounts loaded in the 1.3 liter steel mill are 83 parts ofTiN, 62 parts of TiB 4.5 parts of Mo, and 1.3 parts of Ni.

The titanium diboride powder used in this composition is commerciallyavailable from Materials for Industry, Inc. This powder has a nitrogenspecific surface area of 1.1 square meters per gram and an oxygencontent of 2.32 percent.

A billet prepared as in Example 1 has a density of about 5 grams percubic centimeter, hardness of about 92.7 on the Rockwell A scale andtransverse rupture strength of about 115,000 pounds per square inch.

The billet is cut with a resin-bonded diamond wheel and polished to givetwo ornamental lustrous golden pieces. The pieces are cemented withepoxy resin to two metal cuff-links.

EXAMPLE 8 The procedure of Example 1 is repeated except that thecomponents are used in amounts to give a composition containing volumepercent niobium nitride, 12 volume percent chromium, and 3 volumepercent iron.

The nibium nitride powder used in this preparation is commerciallyavailable, grade -325 mesh, from Cerac, Inc., Butler, Wis. The powder is99.5 percent pure.

The chromium metal powder used in this preparation is available fromMaterials for Industry, Inc. The powder is 99.9 percent pure and theparticle size is 1 to 5 microns, as measured by the Fisher Sub-SieveSizer. Nitrogen specific surface area is 0.8 square meter per gram, andoxygen content 0.79 percent. An electron micrograph of this powder showsdense particles, generally with smooth edges and only some scalloped.edges, and size between 1 and 4 microns. Most of the particles arearound 2 microns in size.

The iron metal powder used in this preparation is available fromMaterials for Industry, Inc., and has a particle size between 1 and 5microns. The powder is 99.9 percent pure.

The actual amounts of components loaded into the 1.3 liter steel millare 214.17 parts of NbN, 24.77 parts of Cr, and 7.06 parts of Fe.

A billet is prepared as in Example 2, having a density of about 8.23grams per cubic centimeter.

The billet of this composition is cut and polished as in Example 5 toobtain /2 inch x /s inch rectangular piece having a golden appearance.The rectangular piece is used as an ornamental inset by cementing itwith epoxy resin on a tie clip.

EXAMPLE 9 The procedure of Example 1 is repeated except that thecomponents are used in amounts to give a composition containing 70volume percent titanium nitride, 27 volume percent tungsten, and 3volume percent nickel.

The actual amounts of components loaded into the 1.3 liter steel millare 118.3 parts of TiN, 162 parts of W metal, and 8.32 parts of Nimetal.

A watch case is fabricated as in Example 1, which has an attractivegolden color.

EXAMPLE 10 The procedure of Example 1 is repeated except that thecomponents are used in amounts to give a composition containing 5 0volume percent titanium nitride, 45 volume percent tantalum carbide, 4.5volume percent tungsten metal and 0.5 volume percent nickel metal.

The tantalum carbide powder used in this preparation is available fromthe Adamas Company and has an average particle size of 3 microns. Thenitrogen surface area is 0.38 squar meter per gram and oxygen content is0.07 percent.

The amounts of components loaded into the 1.3 liter steel mill are 81.46parts of TiN, 197.76 parts of TaC, 25.60 parts of W metal, and 13.03parts of Ni metal.

A watch case is fabricated as in Example 1, which has a golden color.

We claim:

1. An article of jewelry comprising a hard polished compositionconsisting essentially of 30 to 99 volume percent of an essentialnitride of titanium, zirconium or their mixtures; O to 45 volume percentof titanium carbide, tantalum carbide, zirconium carbide, titaniumdiboride or their mixtures; 0 to 70 volume percent of an electricallynon-conducting component selected from among aluminum nitride, aluminaand their mixtures; and to 50 volume ercent of a metal selected fromamong chromium, molybdenum, tungsten, iron, cobalt, nickel, titanium,zirconium, niobium, tantalum, hafnium and their mixtures; saidcomposition having a density of less than 9 grams per cubic centimeter,a porosity of less than percent, an average grain size of less thanmicrons, a resistance to perspiration corrosion and a ratio of lightreflectance at 555 milimicrons to that at 450 millimicrons of between1.1/1 and 1.6/1.

2. An article of claim 1 in which the composition has a porosity of lessthan 1 percent and an average grain size of less than 2 microns.

3. An article of claim 1 in which the essential nitride is present inamounts of 30 to 99 volume percent and the metal is present in amountsof 1 to 50 volume percent.

4. An article of claim 1 in which the composition consists essentiallyof 40 to 80 volume percent essential nitride; 0 to 45 volume percenttitanium carbide, tantalum carbide, zirconium carbide or titaniumdiboride; 0 to 50 volume percent electrically nonconducting componentand 1 to 20 volume percent of metal.

5. An article of claim 1 in which the ratio of light reflectance isbetween 1.15/1 and 1.5/1.

6. An article of claim 5 in which the composition consists essentiallyof 50 to 75 volume percent of an essential nitride selected from amongtitanium nirtide, zirconium nitride and their mixtures; 0 to 35 volumepercent of an electrically non-conducting component selected from amongaluminum nitride and alumina; 0 to 45 volume percent of titaniumdiboride or a carbide selected fdom among titanium carbide, tantalumcarbide, zirconium carbide, and their mixtures; and from 5 to volumepercent of metal selected from among molybdenum, tungsten and theirmixtures with iron, cobalt or nickel.

7. An article of claim 6 wherein the essential nitride is titaniumnitride, the boride or carbide is titanium carbide and the metal isselected from among molybdenum, tungsten and their mixtures with nickel.

8. In a watch case the improvement comprising said case having anexposed outer area comprising a hard polished composition consistingessentially of 30 to 80 volume percent of an essential nitride oftitanium, zirconium or their mixtures; 0 to 45 volume percent oftitanium carbide, tantalum carbide, zirconium carbide, titanium diborideor their mixtures; 0 to 70 volume percent of an electricallynon-conducting component selected from among aluminum nitride, aluminaand their mixtures; and 0 to 50 volume percent of a metal selected fromamong chromium, molybdenum, tungsten, iron, cobalt, nickel, titanium,zirconium, niobium, tantalum, hafnium and their mixtures; saidcomposition having a density of less than 9 grams per cubic centimeter,a porosity of less than 5 percent, an averagegrain size of less than 10microns, a resistance to perspiration corrosion and a ratio of lightreflectance at 555 millimicrons to that at 450 millimicrons of between1.1/1 and 1.6/1.

9. A watch case of claim 8 in which the composition has a porosity ofless than 1 percent and an average grain size of less than 2 microns.

10. A watch case of claim 8 in which the metal is present in amounts of1 to 50 volume percent.

11. A watch case of claim 8 in which the composition consists of 40 to80 volume percent essential nitride; O to 50 volume percent electricallynon-conducting component and 1 to 20 volume percent of metal.

12. A watch case of claim 8 in which the ratio of light reflectance isbetween 1.15/1 and 1.5/ 1.

13. A watch case of claim 12 in which the composition consistsessentially of 50 to volume percent of an essential nitride selectedfrom among titanium nitride, zirconium nitride and their mixtures; 0 to35 volume percent of an electrically non-conducting component selectedfrom among aluminum nitride and alumina; 0 to 45 volume percent oftitanium diboride and from 5 to 15 volume percent of metal selected fromamong molybdenum, tungsten and their mixtures with iron, cobalt ornickel.

14. A watch case of claim 13 in which the essential nitride is titaniumnitride and the metal is selected from among molybdenum, tungsten andtheir mixtures with nickel.

References Cited UNITED STATES PATENTS 3,032,397 5/ 1962; Niederhauser106-299 X 3,205,084 9/1965 Klein et a1. 106299 X 3,242,664 3/ 1966Le'derrey 2888 3,409,416 11/1968 Yates 29182.5 3,409,417 11/1968 Yates29182.5 3,409,418 11/1968 Yates 29182.5 3,409,419 11/1968 Yates 29182.5

FOREIGN PATENTS 1,808,600 7/1969 Germany 106-43 TOBIAS E. LEVOW, PrimaryExaminer W. R. SATIERFIELD, Assistant Examiner US. Cl. XJR.

